The present invention relates generally to data transmission and, in particular, to interleaving during data transmission.
Communication systems take many forms. In general, the purpose of a communication system to transmit information-bearing signals from a source, located at one point, to a user destination, located at another point some distance away. A communication system generally consists of three basic components: transmitter, channel, and receiver. The transmitter has the function of processing the message signal into a form suitable for transmission over the channel. This processing of the message signal is referred to as modulation. The function of the channel is to provide a physical connection between the transmitter output and the receiver input. The function of the receiver is to process the received signal so as to produce an estimate of the original message signal. This processing of the received signal is referred to as demodulation.
Analog and digital transmission methods are used to transmit a message signal over a communication channel. The use of digital methods offers several operational advantages over analog methods, including but not limited to: increased immunity to channel noise and interference, flexible operation of the system, common format for the transmission of different kinds of message signals, improved security of communication through the use of encryption and increased capacity.
With digital communication, user information such as speech is encoded into sequences of binary information symbols. This encoding is convenient for modulation and is easily error-correction coded for transmission over a potentially degrading communication channel. In order to deliver reliable information in a noisy environment, many techniques (e.g., convolutional encoding, interleaving at the symbol level, . . . , etc.) are utilized to improve the quality of the demodulated signal. Although these techniques greatly improve the reliability of information transmitted, situations exist where current techniques are inadequate to provide reliable information in noisy environments. For example, prior-art techniques for interleaving include randomly generating an interleaving address table. This technique has a disadvantage that entire interleaving tables for different data lengths have to be stored in both transmitters and receivers. Consequently there exists a need for a method and apparatus for interleaving within a communication system that requires minimum storage for variable data length.